/*
 *			    C P P 5 . C
 *		E x p r e s s i o n   E v a l u a t i o n
 *
 * Edit History
 * 31-Aug-84	MM	USENET net.sources release
 * 04-Oct-84	MM	__LINE__ and __FILE__ must call ungetstring()
 *			so they work correctly with token concatenation.
 *			Added string formal recognition.
 * 25-Oct-84	MM	"Short-circuit" evaluate #if's so that we
 *			don't print unnecessary error messages for
 *			#if !defined(FOO) && FOO != 0 && 10 / FOO ...
 * 31-Oct-84	ado/MM	Added token concatenation
 *  6-Nov-84	MM	Split from #define stuff, added sizeof stuff
 * 19-Nov-84	ado	#if error returns TRUE for (sigh) compatibility
 */

#include	<stdio.h>
#include	<ctype.h>
#include	<string.h>
#include	"cppdef.h"
#include	"cpp.h"

/*
 * Evaluate an #if expression.
 */

static char	*opname[] = {		/* For debug and error messages	*/
"end of expression", "val", "id",
  "+",   "-",  "*",  "/",  "%",
  "<<", ">>",  "&",  "|",  "^",
  "==", "!=",  "<", "<=", ">=",  ">",
  "&&", "||",  "?",  ":",  ",",
  "unary +", "unary -", "~", "!",  "(",  ")", "(none)",
};

/*
 * opdope[] has the operator precedence:
 *     Bits
 *	  7	Unused (so the value is always positive)
 *	6-2	Precedence (000x .. 017x)
 *	1-0	Binary op. flags:
 *	    01	The binop flag should be set/cleared when this op is seen.
 *	    10	The new value of the binop flag.
 * Note:  Expected, New binop
 * constant	0	1	Binop, end, or ) should follow constants
 * End of line	1	0	End may not be preceeded by an operator
 * binary	1	0	Binary op follows a value, value follows.
 * unary	0	0	Unary op doesn't follow a value, value follows
 *   (		0	0	Doesn't follow value, value or unop follows
 *   )		1	1	Follows value.  Op follows.
 */

static char	opdope[OP_MAX] = {
  0001,					/* End of expression		*/
  0002,					/* Digit			*/
  0000,					/* Letter (identifier)		*/
  0141, 0141, 0151, 0151, 0151,		/* ADD, SUB, MUL, DIV, MOD	*/
  0131, 0131, 0101, 0071, 0071,		/* ASL, ASR, AND,  OR, XOR	*/
  0111, 0111, 0121, 0121, 0121,	0121,	/*  EQ,  NE,  LT,  LE,  GE,  GT	*/
  0061, 0051, 0041, 0041, 0031,		/* ANA, ORO, QUE, COL, CMA	*/
/*
 * Unary op's follow
 */
  0160, 0160, 0160, 0160,		/* NEG, PLU, COM, NOT		*/
  0170, 0013, 0023,			/* LPA, RPA, END		*/
};
/*
 * OP_QUE and OP_RPA have alternate precedences:
 */
#define	OP_RPA_PREC	0013
#define OP_QUE_PREC	0034

/*
 * S_ANDOR and S_QUEST signal "short-circuit" boolean evaluation, so that
 *	#if FOO != 0 && 10 / FOO ...
 * doesn't generate an error message.  They are stored in optab.skip.
 */
#define S_ANDOR		2
#define S_QUEST		1

typedef struct optab {
    char	op;			/* Operator			*/
    char	prec;			/* Its precedence		*/
    char	skip;			/* Short-circuit: TRUE to skip	*/
} OPTAB;
static int	evalue;			/* Current value from evallex()	*/

#ifdef	nomacargs
FILE_LOCAL int
isbinary(op)
register int	op;
{
	return (op >= FIRST_BINOP && op <= LAST_BINOP);
}

FILE_LOCAL int
isunary(op)
register int	op;
{
	return (op >= FIRST_UNOP && op <= LAST_UNOP);
}
#else
#define	isbinary(op)	(op >= FIRST_BINOP && op <= LAST_BINOP)
#define	isunary(op)	(op >= FIRST_UNOP  && op <= LAST_UNOP)
#endif

/*
 * The following definitions are used to specify basic variable sizes.
 */

#ifndef	S_CHAR
#define	S_CHAR		(sizeof (char))
#endif
#ifndef	S_SINT
#define	S_SINT		(sizeof (short int))
#endif
#ifndef	S_INT
#define	S_INT		(sizeof (int))
#endif
#ifndef	S_LINT
#define	S_LINT		(sizeof (long int))
#endif
#ifndef	S_FLOAT
#define	S_FLOAT		(sizeof (float))
#endif
#ifndef	S_DOUBLE
#define	S_DOUBLE	(sizeof (double))
#endif
#ifndef	S_PCHAR
#define	S_PCHAR		(sizeof (char *))
#endif
#ifndef	S_PSINT
#define	S_PSINT		(sizeof (short int *))
#endif
#ifndef	S_PINT
#define	S_PINT		(sizeof (int *))
#endif
#ifndef	S_PLINT
#define	S_PLINT		(sizeof (long int *))
#endif
#ifndef	S_PFLOAT
#define	S_PFLOAT	(sizeof (float *))
#endif
#ifndef	S_PDOUBLE
#define	S_PDOUBLE	(sizeof (double *))
#endif
#ifndef	S_PFPTR
#define S_PFPTR		(sizeof (int (*)()))
#endif

typedef struct types {
    short	type;			/* This is the bit if		*/
    char	*name;			/* this is the token word	*/
} TYPES;

static TYPES basic_types[] = {
	{ T_CHAR,	"char",		},
	{ T_INT,	"int",		},
	{ T_FLOAT,	"float",	},
	{ T_DOUBLE,	"double",	},
	{ T_SHORT,	"short",	},
	{ T_LONG,	"long",		},
	{ T_SIGNED,	"signed",	},
	{ T_UNSIGNED,	"unsigned",	},
	{ 0,		NULL,		},	/* Signal end		*/
};

/*
 * Test_table[] is used to test for illegal combinations.
 */
static short test_table[] = {
	T_FLOAT | T_DOUBLE | T_LONG | T_SHORT,
	T_FLOAT | T_DOUBLE | T_CHAR | T_INT,
	T_FLOAT | T_DOUBLE | T_SIGNED | T_UNSIGNED,
	T_LONG  | T_SHORT  | T_CHAR,
	0						/* end marker	*/
};

/*
 * The order of this table is important -- it is also referenced by
 * the command line processor to allow run-time overriding of the
 * built-in size values.  The order must not be changed:
 *	char, short, int, long, float, double (func pointer)
 */
SIZES size_table[] = {
    { T_CHAR,	S_CHAR,		S_PCHAR		},	/* char		*/
    { T_SHORT,	S_SINT,		S_PSINT		},	/* short int	*/
    { T_INT,	S_INT,		S_PINT		},	/* int		*/
    { T_LONG,	S_LINT,		S_PLINT		},	/* long		*/
    { T_FLOAT,	S_FLOAT,	S_PFLOAT	},	/* float	*/
    { T_DOUBLE,	S_DOUBLE,	S_PDOUBLE	},	/* double	*/
    { T_FPTR,	0,		S_PFPTR		},	/* int (*()) 	*/
    { 0,	0,		0		},	/* End of table	*/
};

int
eval()
/*
 * Evaluate an expression.  Straight-forward operator precedence.
 * This is called from control() on encountering an #if statement.
 * It calls the following routines:
 * evallex	Lexical analyser -- returns the type and value of
 *		the next input token.
 * evaleval	Evaluate the current operator, given the values on
 *		the value stack.  Returns a pointer to the (new)
 *		value stack.
 * For compatiblity with older cpp's, this return returns 1 (TRUE)
 * if a syntax error is detected.
 */
{
	register int	op;		/* Current operator		*/
	register int	*valp;		/* -> value vector		*/
	register OPTAB	*opp;		/* Operator stack		*/
	int		prec;		/* Op precedence		*/
	int		binop;		/* Set if binary op. needed	*/
	int		op1;		/* Operand from stack		*/
	int		skip;		/* For short-circuit testing	*/
	int		value[NEXP];	/* Value stack			*/
	OPTAB		opstack[NEXP];	/* Operand stack		*/
	extern int	*evaleval();	/* Does actual evaluation	*/

	valp = value;
	opp = opstack;
	opp->op = OP_END;		/* Mark bottom of stack		*/
	opp->prec = opdope[OP_END];	/* And its precedence		*/
	opp->skip = 0;			/* Not skipping now		*/
	binop = 0;
again:	;
#ifdef	DEBUG_EVAL
	printf("In #if at again: skip = %d, binop = %d, line is: %s",
	    opp->skip, binop, infile->bptr);
#endif
	if ((op = evallex(opp->skip)) == OP_SUB && binop == 0)
	    op = OP_NEG;			/* Unary minus		*/
	else if (op == OP_ADD && binop == 0)
	    op = OP_PLU;			/* Unary plus		*/
	else if (op == OP_FAIL)
	    return (1);				/* Error in evallex	*/
#ifdef	DEBUG_EVAL
	printf("op = %s, opdope = %03o, binop = %d, skip = %d\n",
	    opname[op], opdope[op], binop, opp->skip);
#endif
	if (op == DIG) {			/* Value?		*/
	    if (binop != 0) {
		cerror("misplaced constant in #if", NULLST);
		return (1);
	    }
	    else if (valp >= &value[NEXP-1]) {
		cerror("#if value stack overflow", NULLST);
		return (1);
	    }
	    else {
#ifdef	DEBUG_EVAL
		printf("pushing %d onto value stack[%d]\n",
		    evalue, valp - value);
#endif
		*valp++ = evalue;
		binop = 1;
	    }
	    goto again;
	}
	else if (op > OP_END) {
	    cerror("Illegal #if line", NULLST);
	    return (1);
	}
	prec = opdope[op];
	if (binop != (prec & 1)) {
	    cerror("Operator %s in incorrect context", opname[op]);
	    return (1);
	}
	binop = (prec & 2) >> 1;
	for (;;) {
#ifdef	DEBUG_EVAL
	    printf("op %s, prec %d., stacked op %s, prec %d, skip %d\n",
		opname[op], prec, opname[opp->op], opp->prec, opp->skip);
#endif
	    if (prec > opp->prec) {
		if (op == OP_LPA)
		    prec = OP_RPA_PREC;
		else if (op == OP_QUE)
		    prec = OP_QUE_PREC;
		op1 = opp->skip;		/* Save skip for test	*/
		/*
		 * Push operator onto op. stack.
		 */
		opp++;
		if (opp >= &opstack[NEXP]) {
		    cerror("expression stack overflow at op \"%s\"",
			opname[op]);
		    return (1);
		}
		opp->op = op;
		opp->prec = prec;
		skip = (valp[-1] != 0);		/* Short-circuit tester	*/
		/*
		 * Do the short-circuit stuff here.  Short-circuiting
		 * stops automagically when operators are evaluated.
		 */
		if ((op == OP_ANA && !skip)
		 || (op == OP_ORO && skip))
		    opp->skip = S_ANDOR;	/* And/or skip starts	*/
		else if (op == OP_QUE)		/* Start of ?: operator	*/
		    opp->skip = (op1 & S_ANDOR) | ((!skip) ? S_QUEST : 0);
		else if (op == OP_COL) {	/* : inverts S_QUEST	*/
		    opp->skip = (op1 & S_ANDOR)
			      | (((op1 & S_QUEST) != 0) ? 0 : S_QUEST);
		}
		else {				/* Other ops leave	*/
		    opp->skip = op1;		/*  skipping unchanged.	*/
		}
#ifdef	DEBUG_EVAL
		printf("stacking %s, valp[-1] == %d at %s",
		    opname[op], valp[-1], infile->bptr);
		dumpstack(opstack, opp, value, valp);
#endif
		goto again;
	    }
	    /*
	     * Pop operator from op. stack and evaluate it.
	     * End of stack and '(' are specials.
	     */
	    skip = opp->skip;			/* Remember skip value	*/
	    switch ((op1 = opp->op)) {		/* Look at stacked op	*/
	    case OP_END:			/* Stack end marker	*/
		if (op == OP_EOE)
		    return (valp[-1]);		/* Finished ok.		*/
		goto again;			/* Read another op.	*/

	    case OP_LPA:			/* ( on stack		*/
		if (op != OP_RPA) {		/* Matches ) on input	*/
		    cerror("unbalanced paren's, op is \"%s\"", opname[op]);
		    return (1);
		}
		opp--;				/* Unstack it		*/
		/* goto again;			-- Fall through		*/

	    case OP_QUE:
		goto again;			/* Evaluate true expr.	*/

	    case OP_COL:			/* : on stack.		*/
		opp--;				/* Unstack :		*/
		if (opp->op != OP_QUE) {	/* Matches ? on stack?	*/
		    cerror("Misplaced '?' or ':', previous operator is %s",
			opname[opp->op]);
		    return (1);
		}
		/*
		 * Evaluate op1.
		 */
	    default:				/* Others:		*/
		opp--;				/* Unstack the operator	*/
#ifdef	DEBUG_EVAL
		printf("Stack before evaluation of %s\n", opname[op1]);
		dumpstack(opstack, opp, value, valp);
#endif
		valp = evaleval(valp, op1, skip);
#ifdef	DEBUG_EVAL
		printf("Stack after evaluation\n");
		dumpstack(opstack, opp, value, valp);
#endif
	    }					/* op1 switch end	*/
	}					/* Stack unwind loop	*/
}

FILE_LOCAL int
evallex(skip)
int		skip;		/* TRUE if short-circuit evaluation	*/
/*
 * Return next eval operator or value.  Called from eval().  It
 * calls a special-purpose routines for 'char' strings and
 * numeric values:
 * evalchar	called to evaluate 'x'
 * evalnum	called to evaluate numbers.
 */
{
	register int	c, c1, t;

again:  do {					/* Collect the token	*/
	    c = skipws();
	    if ((c = macroid(c)) == EOF_CHAR || c == '\n') {
		unget();
		return (OP_EOE);		/* End of expression	*/
	    }
	} while ((t = type[c]) == LET && catenate());
	if (t == INV) {				/* Total nonsense	*/
	    if (!skip) {
		if (isascii(c) && isprint(c))
		    cierror("illegal character '%c' in #if", c);
		else
		    cierror("illegal character (%d decimal) in #if", c);
	    }
	    return (OP_FAIL);
	}
	else if (t == QUO) {			/* ' or "		*/
	    if (c == '\'') {			/* Character constant	*/
		evalue = evalchar(skip);	/* Somewhat messy	*/
#ifdef	DEBUG_EVAL
		printf("evalchar returns %d.\n", evalue);
#endif
		return (DIG);			/* Return a value	*/
	    }
	    cerror("Can't use a string in an #if", NULLST);
	    return (OP_FAIL);
	}
	else if (t == LET) {			/* ID must be a macro	*/
	    if (streq(token, "defined")) {	/* Or defined name	*/
		c1 = c = skipws();
		if (c == '(')			/* Allow defined(name)	*/
		    c = skipws();
		if (type[c] == LET) {
		    evalue = (lookid(c) != NULL);
		    if (c1 != '('		/* Need to balance	*/
		     || skipws() == ')')	/* Did we balance?	*/
			return (DIG);		/* Parsed ok		*/
		}
		cerror("Bad #if ... defined() syntax", NULLST);
		return (OP_FAIL);
	    }
	    else if (streq(token, "sizeof"))	/* New sizeof hackery	*/
		return (dosizeof());		/* Gets own routine	*/
	    /*
	     * The Draft ANSI C Standard says that an undefined symbol
	     * in an #if has the value zero.  We are a bit pickier,
	     * warning except where the programmer was careful to write
	     * 		#if defined(foo) ? foo : 0
	     */
#ifdef STRICT_UNDEF
	    if (!skip)
		cwarn("undefined symbol \"%s\" in #if, 0 used", token);
#endif
	    evalue = 0;
	    return (DIG);
	}
	else if (t == DIG) {			/* Numbers are harder	*/
	    evalue = evalnum(c);
#ifdef	DEBUG_EVAL
	    printf("evalnum returns %d.\n", evalue);
#endif
	}
	else if (strchr("!=<>&|\\", c) != NULL) {
	    /*
	     * Process a possible multi-byte lexeme.
	     */
	    c1 = cget();			/* Peek at next char	*/
	    switch (c) {
	    case '!':
		if (c1 == '=')
		    return (OP_NE);
		break;

	    case '=':
		if (c1 != '=') {		/* Can't say a=b in #if	*/
		    unget();
		    cerror("= not allowed in #if", NULLST);
		    return (OP_FAIL);
		}
		return (OP_EQ);

	    case '>':
	    case '<':
		if (c1 == c)
		    return ((c == '<') ? OP_ASL : OP_ASR);
		else if (c1 == '=')
		    return ((c == '<') ? OP_LE  : OP_GE);
		break;

	    case '|':
	    case '&':
		if (c1 == c)
		    return ((c == '|') ? OP_ORO : OP_ANA);
		break;

	    case '\\':
		if (c1 == '\n')			/* Multi-line if	*/
		    goto again;
		cerror("Unexpected \\ in #if", NULLST);
		return (OP_FAIL);
	    }
	    unget();
	}
	return (t);
}

FILE_LOCAL int
dosizeof()
/*
 * Process the sizeof (basic type) operation in an #if string.
 * Sets evalue to the size and returns
 *	DIG		success
 *	OP_FAIL		bad parse or something.
 */
{
	register int	c;
	register TYPES	*tp;
	register SIZES	*sizp;
	register short	*testp;
	short		typecode;

	if ((c = skipws()) != '(')
	    goto nogood;
	/*
	 * Scan off the tokens.
	 */
	typecode = 0;
	while ((c = skipws())) {
	    if ((c = macroid(c)) == EOF_CHAR || c == '\n')
		goto nogood;			/* End of line is a bug	*/
	    else if (c == '(') {		/* thing (*)() func ptr	*/
		if (skipws() == '*'
		 && skipws() == ')') {		/* We found (*)		*/
		    if (skipws() != '(')	/* Let () be optional	*/
			unget();
		    else if (skipws() != ')')
			goto nogood;
		    typecode |= T_FPTR;		/* Function pointer	*/
		}
		else {				/* Junk is a bug	*/
		    goto nogood;
		}
	    }
	    else if (type[c] != LET)		/* Exit if not a type	*/
		break;
	    else if (!catenate()) {		/* Maybe combine tokens	*/
		/*
		 * Look for this unexpandable token in basic_types.
		 * The code accepts "int long" as well as "long int"
		 * which is a minor bug as bugs go (and one shared with
		 * a lot of C compilers).
		 */
		for (tp = basic_types; tp->name != NULLST; tp++) {
		    if (streq(token, tp->name))
			break;
		}
		if (tp->name == NULLST) {
		    cerror("#if sizeof, unknown type \"%s\"", token);
		    return (OP_FAIL);
		}
		typecode |= tp->type;		/* Or in the type bit	*/
	    }
	}
	/*
	 * We are at the end of the type scan.  Chew off '*' if necessary.
	 */
	if (c == '*') {
	    typecode |= T_PTR;
	    c = skipws();
	}
	if (c == ')') {				/* Last syntax check	*/
	    for (testp = test_table; *testp != 0; testp++) {
		if (!bittest(typecode & *testp)) {
		    cerror("#if ... sizeof: illegal type combination", NULLST);
		    return (OP_FAIL);
		}
	    }
	    /*
	     * We assume that all function pointers are the same size:
	     *		sizeof (int (*)()) == sizeof (float (*)())
	     * We assume that signed and unsigned don't change the size:
	     *		sizeof (signed int) == (sizeof unsigned int)
	     */
	    if ((typecode & T_FPTR) != 0)	/* Function pointer	*/
		typecode = T_FPTR | T_PTR;
	    else {				/* Var or var * datum	*/
		typecode &= ~(T_SIGNED | T_UNSIGNED);
		if ((typecode & (T_SHORT | T_LONG)) != 0)
		    typecode &= ~T_INT;
	    }
	    if ((typecode & ~T_PTR) == 0) {
		cerror("#if sizeof() error, no type specified", NULLST);
		return (OP_FAIL);
	    }
	    /*
	     * Exactly one bit (and possibly T_PTR) may be set.
	     */
	    for (sizp = size_table; sizp->bits != 0; sizp++) {
		if ((typecode & ~T_PTR) == sizp->bits) {
		    evalue = ((typecode & T_PTR) != 0)
			? sizp->psize : sizp->size;
		    return (DIG);
		}
	    }					/* We shouldn't fail	*/
	    cierror("#if ... sizeof: bug, unknown type code 0x%x", typecode);
	    return (OP_FAIL);
	}

nogood:	unget();
	cerror("#if ... sizeof() syntax error", NULLST);
	return (OP_FAIL);
}

FILE_LOCAL int
bittest(value)
/*
 * TRUE if value is zero or exactly one bit is set in value.
 */
{
#if (4096 & ~(-4096)) == 0
	return ((value & ~(-value)) == 0);
#else
	/*
	 * Do it the hard way (for non 2's complement machines)
	 */
	return (value == 0 || value ^ (value - 1) == (value * 2 - 1));
#endif
}

FILE_LOCAL int
evalnum(c)
register int	c;
/*
 * Expand number for #if lexical analysis.  Note: evalnum recognizes
 * the unsigned suffix, but only returns a signed int value.
 */
{
	register int	value;
	register int	base;
	register int	c1;

	if (c != '0')
	    base = 10;
	else if ((c = cget()) == 'x' || c == 'X') {
		base = 16;
		c = cget();
	}
	else base = 8;
	value = 0;
	for (;;) {
	    c1 = c;
	    if (isascii(c) && isupper(c1))
		c1 = tolower(c1);
	    if (c1 >= 'a')
		c1 -= ('a' - 10);
	    else c1 -= '0';
	    if (c1 < 0 || c1 >= base)
		break;
	    value *= base;
	    value += c1;
	    c = cget();
	}
	/* Formerly unsigned nonsense, now good luck */
	if (c == 'u' || c == 'U' || c == 'l' || c == 'L') 
	    c = cget();
	unget();
	return (value);
}

FILE_LOCAL int
evalchar(skip)
int		skip;		/* TRUE if short-circuit evaluation	*/
/*
 * Get a character constant
 */
{
	register int	c;
	register int	value;
	register int	count;

	instring = TRUE;
	if ((c = cget()) == '\\') {
	    switch ((c = cget())) {
	    case 'a':				/* New in Standard	*/
#if ('a' == '\a' || '\a' == ALERT)
		value = ALERT;			/* Use predefined value	*/
#else
		value = '\a';			/* Use compiler's value	*/
#endif
		break;

	    case 'b':
		value = '\b';
		break;

	    case 'f':
		value = '\f';
		break;

	    case 'n':
		value = '\n';
		break;

	    case 'r':
		value = '\r';
		break;

	    case 't':
		value = '\t';
		break;

	    case 'v':				/* New in Standard	*/
#if ('v' == '\v' || '\v' == VT)
		value = VT;			/* Use predefined value	*/
#else
		value = '\v';			/* Use compiler's value	*/
#endif
		break;

	    case 'x':				/* '\xFF'		*/
		count = 3;
		value = 0;
		while ((((c = get()) >= '0' && c <= '9')
		     || (c >= 'a' && c <= 'f')
		     || (c >= 'A' && c <= 'F'))
		    && (--count >= 0)) {
			value *= 16;
			value += (c <= '9') ? (c - '0') : ((c & 0xF) + 9);
		}
		unget();
		break;

	    default:
		if (c >= '0' && c <= '7') {
		    count = 3;
		    value = 0;
		    while (c >= '0' && c <= '7' && --count >= 0) {
			value *= 8;
			value += (c - '0');
			c = get();
		    }
		    unget();
		}
		else value = c;
		break;
	    }
	}
	else if (c == '\'')
	    value = 0;
	else value = c;
	/*
	 * We warn on multi-byte constants and try to hack
	 * (big|little)endian machines.
	 */
#if BIG_ENDIAN
	count = 0;
#endif
	while ((c = get()) != '\'' && c != EOF_CHAR && c != '\n') {
	    if (!skip)
		ciwarn("multi-byte constant '%c' isn't portable", c);
#if BIG_ENDIAN
	    count += BITS_CHAR;
	    value += (c << count);
#else
	    value <<= BITS_CHAR;
	    value += c;
#endif
	}
	instring = FALSE;
	return (value);
}

FILE_LOCAL int *
evaleval(valp, op, skip)
register int	*valp;
int		op;
int		skip;		/* TRUE if short-circuit evaluation	*/
/*
 * Apply the argument operator to the data on the value stack.
 * One or two values are popped from the value stack and the result
 * is pushed onto the value stack.
 *
 * OP_COL is a special case.
 *
 * evaleval() returns the new pointer to the top of the value stack.
 */
{
	register int	v1, v2;

	if (isbinary(op))
	    v2 = *--valp;
	v1 = *--valp;
#ifdef	DEBUG_EVAL
	printf("%s op %s", (isbinary(op)) ? "binary" : "unary",
	    opname[op]);
	if (isbinary(op))
	    printf(", v2 = %d.", v2);
	printf(", v1 = %d.\n", v1);
#endif
	switch (op) {
	case OP_EOE:
	     break;

	case OP_ADD:
	    v1 += v2;
	    break;

	case OP_SUB:
	    v1 -= v2;
	    break;

	case OP_MUL:
	    v1 *= v2;
	    break;

	case OP_DIV:
	case OP_MOD:
	    if (v2 == 0) {
		if (!skip) {
		    cwarn("%s by zero in #if, zero result assumed",
			(op == OP_DIV) ? "divide" : "mod");
		}
		v1 = 0;
	    }
	    else if (op == OP_DIV)
		v1 /= v2;
	    else
		v1 %= v2;
	    break;

	case OP_ASL:
	    v1 <<= v2;
	    break;

	case OP_ASR:
	    v1 >>= v2;
	    break;

	case OP_AND:
	    v1 &= v2;
	    break;

	case OP_OR:
	    v1 |= v2;
	    break;

	case OP_XOR:
	    v1 ^= v2;
	    break;

	case OP_EQ:
	    v1 = (v1 == v2);
	    break;

	case OP_NE:
	    v1 = (v1 != v2);
	    break;

	case OP_LT:
	    v1 = (v1 < v2);
	    break;

	case OP_LE:
	    v1 = (v1 <= v2);
	    break;

	case OP_GE:
	    v1 = (v1 >= v2);
	    break;

	case OP_GT:
	    v1 = (v1 > v2);
	    break;

	case OP_ANA:
	    v1 = (v1 && v2);
	    break;

	case OP_ORO:
	    v1 = (v1 || v2);
	    break;

	case OP_COL:
	    /*
	     * v1 has the "true" value, v2 the "false" value.
	     * The top of the value stack has the test.
	     */
	    v1 = (*--valp) ? v1 : v2;
	    break;

	case OP_NEG:
	    v1 = (-v1);
	    break;

	case OP_PLU:
	    break;

	case OP_COM:
	    v1 = ~v1;
	    break;

	case OP_NOT:
	    v1 = !v1;
	    break;

	default:
	    cierror("#if bug, operand = %d.", op);
	    v1 = 0;
	}
	*valp++ = v1;
	return (valp);
}

#ifdef	DEBUG_EVAL
dumpstack(opstack, opp, value, valp)
OPTAB		opstack[NEXP];	/* Operand stack		*/
register OPTAB	*opp;		/* Operator stack		*/
int		value[NEXP];	/* Value stack			*/
register int	*valp;		/* -> value vector		*/
{
	printf("index op prec skip name -- op stack at %s", infile->bptr);
	while (opp > opstack) {
	    printf(" [%2d] %2d  %03o    %d %s\n", opp - opstack,
		opp->op, opp->prec, opp->skip, opname[opp->op]);
	    opp--;
	}
	while (--valp >= value) {
	    printf("value[%d] = %d\n", (valp - value), *valp);
	}
}
#endif

